1. Field of the Invention
The invention concerns an electrostatic method and device for the spraying of liquid or powder and in particular concerns an improvement of the means of electrostatically charging a coating material permitting an optimal and even coating thickness to be obtained whatever the shape of the object being coated.
The invention also permits the transfer efficiency to be improved with respect to that obtained with classical devices thus resulting in a saving in the coating material.
2. Description of the Prior Art
In known devices, the coating material is electrostatically charged by one or several electrodes so as to follow the lines of the electrostatic field between the spraying device and the object to be coated. The charge can be carried out by contact of the material with the electrode or by a Corona discharge of the electrode. In the two cases, the intensity of the electric force undergone by each particle of the coating material, depends on the charge borne by the particle and on the ambient electrostatic field. The latter is a function, among others, of the geometrical configuration of the object to be coated. In fact, if the sharp edge of an object is placed facing the spraying device, the lines of the field all have a tendency to close themselves around this edge. As the particles are guided by the electrostatic field, this leads to an accumulation of the material in this spot while the flat surfaces next to the edge are not coated sufficiently. In the same way, in the case of an object with a cavity, the electrostatic field lines have a tendency to close themselves around the edges of the cavities which tends to prevent the coating material from penetrating into the bottom of the cavity in question.
The invention solves all these problems.